127 



mens which I have seen having been captured (the first 

 by myself, in 1849 ; and the second by the Rev. R. T. 

 Lowe, in 1850) on the respective summits of the Middle 

 and Southern Dezertas. So local indeed does it seem to 

 be, that it, apparently, has not extended itself even over 

 the Dezerta Grande (where there are no external ob- 

 stacles to bar its progress) ; but retains the very position 

 which in all probability constituted its original centre of 

 dissemination at the remote period of time when this 

 ancient continent received its allotted forms. Judging 

 from the slowness with which creatures of such habits 

 must necessarily, under any circumstances, be diffused, 

 it is at least unlikely that the present one could have 

 circulated far, when the now submerged portions of that 

 region began to give way; and hence it is not impossible 

 that the Southern Dezerta, with the adjacent part (then 

 united to it) of the Central one, may have embraced the 

 whole area of its actual primseval range, the remains 

 of which (though they be now separated by a channel) it 

 still continues to occupy, and from which, even when 

 physically unimpeded, it has never roamed*." 



Although it is not my province in this volume to draw 

 inferences from data which are not strictly entomologi- 

 cal, I shall perhaps be pardoned for adding a few words 

 on the testimony which the Land Mollusca of the 

 Madeiras would seem to afford, in support of the general 

 slowness of the animal migrations over that primseval 

 continent. The researches of the Rev. R. T. Lowe, and 

 * Insecta Maderensia, p. 435. 



